The present invention relates generally to the field of skewed roller brake assemblies, and, more particularly, to an improved skewed roller brake assembly that allows different braking characteristics depending upon the direction of relative rotation between facing first and second plates.
Skewed roller brake assemblies are known as a class of rotary braking devices which develop friction between a pair of relatively-rotating axially-loaded disks by means of rollers carried in a slotted plate between the disks. The slots containing the rollers are arranged at a skew angle relative to radii from the center of rotation so that, as the rollers roll between the disks, they tend to track inwardly or outwardly on the disk surfaces. However, the rollers are constrained to maintain a constant radius about the centerline of the brake, causing an axial sliding along the line of rolling contact. This combination of rolling and sliding contact has the desirable property of lending to equalize breakout and running friction, thereby avoiding erratic brake behavior.
Basically, these devices generally contemplate that a plurality of rollers, arranged in a circular array, be disposed between two facing annular plates. The rollers are restrained in slots provided in an intermediate plate positioned between the first and second plates. In known prior art forms, the intermediate plate slots are generally rectangular, and are arranged to closely embrace the roller therewithin. Thus, the skew angle of the roller axis is substantially the same regardless of the direction of relative rotation between the plates.
Specific details of such known prior art skewed roller brake assemblies are representatively shown and described in U.S. Pat. Nos. 4,850,458 and 6,109,415, the aggregate disclosures of which are hereby incorporated by reference. In some applications of skewed roller brake elements, it is desirable to produce one value of braking coefficient in one direction of relative rotation, and another value (possibly approaching zero) in the opposite direction. This could be achieved by means of different braking elements, coupled through over-running clutches or opposed ratchets, such as shown in the aforesaid U.S. Pat. No. 6,109,415.
The present invention offers the desirable property of providing differing coefficients of braking friction inherent in the braking assembly as a function of the direction of relative rotation, without the need for additional clutches or ratchets.
The present invention provides an improvement in a skewed roller brake assembly (20). Such a brake assembly has a main axis of rotation (xxe2x80x94x), has a first plate (21) adapted to be rotated about the main axis, has a second plate (22) adapted to be rotated relative to the first plate about the main axis, and has an intermediate plate (23) positioned between the first and second plates and also arranged to rotate about the main axis. The first and second plates are adapted to be axially loaded by a braking force Fxe2x80x94F with respect to one another. The intermediate plate has a slot 24 bounded by a first wall (26) that is arranged at a first angle xcex81 with respect to a radius from the main axis, and has a cylindrical roller (25) arranged in the slot for rolling engagement with the first and second plates about the axis (yxe2x80x94y) of the roller such that the roller axis is parallel to the first wall when the first and second plates are rotated relative to one another in one angular direction. The improvement broadly comprises; the slot having a second wall (28) arranged at a second angle (xcex82) with respect to a radius from the main axis such that the roller axis is substantially parallel to the second wall when the first and second plates are rotated relative to one another in the opposite angular direction; whereby the resistance to relative rotation between the first and second plates for the same value of axially loading may differ as a function of the direction of relative angular rotation between the first and second plates.
In the preferred embodiment, the second wall is substantially parallel to a radius from the main axis. The roller is mounted in the slot for movement between the first and second walls. The intermediate plate may have a plurality of such slots, and the assembly may include a corresponding plurality of such rollers, with one of the rollers being arranged in one of the slots. Each roller is restrained from moving axially by the end faces of the slots when the roller axis is parallel to either the first wall or to the second wall.
Accordingly, the general object of the invention is to provide an improved skewed roller brake assembly.
Another object is to provide an improved skewed roller brake assembly which affords different degrees of rolling resistance depending upon the direction of relative angular rotation between two facing plates.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims.